将数据与数据库

Question

我想比较用户点击购买东西时数据库中的数据，数据会与数据库进行比较。如果用户患有此病，则不允许用户购买。任何人都可以检查我的代码是否有任何错误？

 private void submit(){
   myRef.child("Users").child(userID).child("medical");
    myRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                if (postSnapshot.child("medical").getValue(String.class) .equals("Diabetes") ) {
                    Toast.makeText(getApplicationContext(), "Diabetes", Toast.LENGTH_SHORT).show();
                    startActivity(new Intent(getApplicationContext(), Medicine.class));
                }else{

                }
            }
        }

  

java.lang.NullPointerException：尝试调用虚方法   ＆＃39; boolean java.lang.String.equals（java.lang.Object）＆＃39;在null对象上   参考                                                                                    在   com.bleach.finalyearproject.Pain_and_Fever $ 1.onDataChange（Pain_and_Fever.java:61

这是用户密钥的页面，其信息和存储在数据库中

 btnSubmit.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            Log.d(TAG, "onClick: Submit pressed.");
            String name = mName.getText().toString();
            String address = mAddress.getText().toString();
            String phoneNum = mPhoneNum.getText().toString();
            String gender = mGender.getText().toString();
            String country = mCountry.getText().toString();
            String medicine = mMedicine.getText().toString();
            String medical = rb.getText().toString();

            startActivity(new Intent(getApplicationContext(),MainActivity.class));

            Log.d(TAG, "onClick: Attempting to submit to database: \n" +
                    "name: " + name + "\n" +
                    "address: " + address + "\n" +
                    "phone number: " + phoneNum + "\n" +
                    "gender: " + gender + "\n" +
                    "country: " + country + "\n" +
                    "medicine: " + medicine + "\n" +
                     "medical:" + medical + "\n"
            );

            //handle the exception if the EditText fields are null

           if(!name.equals("") && !address.equals("") && !phoneNum.equals("") && !gender.equals("") && !country.equals("") && !medicine.equals("")){
                UserInformation userInformation = new UserInformation(name,address,phoneNum,gender,country,medicine,medical);
                myRef.child("Users").child(userID).setValue(userInformation);
                toastMessage("Information has been saved.");
                mName.setText("");
                mAddress.setText("");
                mPhoneNum.setText("");
                mGender.setText("");
                mCountry.setText("");
                mMedicine.setText("");
                rb.setText("");
                startActivity(new Intent(getApplicationContext(),LoginActivity.class));


            }else{
                toastMessage("Fill out all the fields");
                startActivity(new Intent(getApplicationContext(),AddToDatabase.class));
            }


        }

    });


        }


public void rbclick(View view){

   int radiobuttonid = rg.getCheckedRadioButtonId();
   rb  = (RadioButton) findViewById(radiobuttonid);
    Toast.makeText(getApplicationContext(),rb.getText(),Toast.LENGTH_SHORT).show();


 }

Answer 1

如果用户有糖尿病，您可以使用查询加载数据：

myRef.child("Users").child(userID)
     .orderByChild("medical").equalTo("Diabetes").addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        if (dataSnapshot.exists()) {
            Toast.makeText(getApplicationContext(), "Diabetes", Toast.LENGTH_SHORT).show();
            startActivity(new Intent(getApplicationContext(), Medicine.class));
        }
    }

或者您可以加载用户并在客户端代码中进行检查：

myRef.child("Users").child(userID)
     .addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        if (dataSnapshot.child("medical").getValue(String.class).equals("Diabetes")) {
            Toast.makeText(getApplicationContext(), "Diabetes", Toast.LENGTH_SHORT).show();
            startActivity(new Intent(getApplicationContext(), Medicine.class));
        }
    }